Vehicles incorporate breath alcohol ignition interlock devices, sometimes abbreviated as BAIIDs, to prevent a driver from operating the vehicle while intoxicated with alcohol. Such devices are designed to prevent a driver from starting a motor vehicle when the driver's breath alcohol concentration (BAC) is at or above a set alcohol concentration. Each state in the U.S. has adopted a law providing for use of such BAIID devices as a sanction for drivers convicted of driving while intoxicated, or as a condition of restoring some driving privileges after such offenses.
In operation, a driver must use a BAIID device by blowing into a portion of the BAIID coupled to an alcohol-sensing element such as a fuel cell that measures the amount of alcohol in the driver's breath, thereby providing a reliable estimate of the blood alcohol concentration in the driver's blood. The BAIID reads a signal from the fuel cell or other alcohol-sensing element, and determines whether the driver's breath alcohol content exceeds a threshold amount. If the driver's blood alcohol content does not exceed the threshold, the driver is determined not to be intoxicated and the BAIID allows the vehicle to start and run by electrically enabling a system within the vehicle, such as the starter, fuel pump, ignition, or the like. If the breath sample delivered has a higher breath alcohol content than a predetermined allowable threshold, the vehicle is not allowed to start, and the BAIID device records a violation.
Repeated use of the BAIID device can contaminate the fuel cell or other alcohol sensing element, causing its sensitivity to ethanol in the user's breath to vary over time. To ensure that the BAIID measures alcohol accurately and consistently, regulations require that the BAIID be recalibrated from time to time, and that the BAIID be able to provide consistent results during and shortly after a stated recalibration interval.
A typical BAIID device meets guidelines established by the National Highway Traffic Safety Administration (NHTSA) in published model specifications for BAIIDs, which specify various tests that such a device must pass to make it an effective and reliable deterrent to intoxicated driving. For example, the model specifies tests designed to ensure a specified minimum volume of breath is delivered at a specified minimum flow rate against less than a specified maximum back pressure to ensure that an accurate result is produced, and specifies how such a device should be installed into a vehicle to prevent the vehicle from operating pending a determination that the driver is not intoxicated. The model also specifies that a device should be able to pass a calibration test within a specified tolerance for at least seven days past its stated recalibration period, which can vary from 30 to 90 days.
Recalibration typically involves recalibrating the BAIID device, or at least the portion of the device containing the fuel cell, in the vehicle or replacing it with a recently-calibrated device. If the BAIID is replaced, the removed device is then sent back to the manufacturer's calibration facility for recalibration, after which it is sent back to an installation or service center to be returned to service in another vehicle. The recalibration process involves using a reference gas having a known concentration of ethanol, such as compressed gas from a tank or gas generated using a wet bath solution. The reference gas is provided to the fuel cell or other alcohol sensing element, and the indicated output of the device is adjusted to correspond to the known ethanol concentration of the reference gas.
This ensures consistent and reliable calibration of the BAIID device, but because shipping the device from and to a service center and calibration can take a week or more, a high percentage of BAIID devices are constantly in transit to and from the manufacturer's service center. A need therefore exists for more efficient calibration of BAIID devices, while ensuring reliable and trackable calibration of the devices.